Surface mount assembly (SMT) has a crucial role to learn from the New service Introduction (NPI) process for electronics manufacturing.
The top amount of automation within the SMT methodology supplies a selection of advantages, from automatic correction of errors, to simpler and faster assembly, better mechanical performance, increased production rates and reduced labour costs.
The SMT assembly process on an electronics manufacturing services (EMS) provider could be divided into four key stages:
Solder Paste Printing
Pick and Place
Oven Profiling
Automated Optical Inspection (AOI)
With regards to the complexity with the design, or your own outsourcing strategy, your product or service could go through all these processes consequently, otherwise you could find that you just omit a step or two.
We want to highlight the particular attributes, as well as the vital importance, in the solder paste printing process for the NPI.
Trying to your specifications
The first task for your EMS provider may be to analyse the pcb (PCB) data that is specific on your order, to make sure that they pick the required stencil thickness and the the best option material.
Solder paste printing is regarded as the common technique of applying solder paste into a PCB. Accurate solder paste application is hugely important in avoiding assembly defects which could have a very knock on effect further along the production process. So it is vital that this key stage is correctly managed and controlled through your EMS partner.
Solder paste is essentially powdered solder which was suspended in a thick medium called flux. The flux provides a form of temporary adhesive, holding the ingredients in position prior to the soldering process begins. Solder paste is used towards the PCB by using a stencil (generally metal, but occasionally nickel,) then when the solder is melted it forms an electrical/mechanical connection.
The thickness with the stencil is the thing that determines the total number of solder applied. For many projects it may be essential to have a lot of thicknesses in different areas within the one stencil (also known as a multi-level stencil).
Another primary factor to think about inside the solder printing process is paste release. The best type of solder paste ought to be selected dependant on the dimensions of the apertures (or holes) from the stencil. If your apertures are very small, for instance, then your solder paste could be more prone to sticking to the stencil rather than adhering correctly for the PCB.
Controlling the rate of paste release however can easily be managed, either by making changes for the style of the aperture or by reduction of the thickness in the stencil.
The type of solder paste which is used also can affect the ultimate print quality, therefore it is imperative that you pick the appropriate combination of solder sphere size and alloy for the project, and also to ensure it is mixed towards the correct consistency before use.
Ensuring quality
When the stencil has become designed and your EMS partner is ready to create the first PCB, they are going to next want to think about machine settings.
Quite simply, the flatter you can keep the PCB over the printing process, the better the end result will likely be. So by fully supporting the PCB in the printing stage,either by way of automated tooling pins or with a dedicated support plate, your EMS provider can remove the potential for any defects like poor paste deposit or smudging.
You’ll want to look at the speed and pressure with the squeegees during the printing process. One solution is usually to have one speed for your solder paste but to have varying numbers of pressure, based on the unique specifications of the PCB and the entire squeegee.
Washing the stencils, both before and throughout production, may also be essential in ensuring qc. Many automatic printing machines have a very system that could be set to completely clean the stencil from a fixed number of prints which will help in order to avoid smudging, and prevents any blockages with the apertures.
Finally too, the printers should have a built-in inspection system (for example Hawk-Eye optical inspection) that may be preset to evaluate the presence of paste throughout the whole PCB after printing.
The solder paste printing process can be a precise and detailed the one which will have a significant part to learn within the ultimate success of one’s new service. And, since this post highlights, so much detailed tasks are more likely to come about behind the curtain before your EMS partner solders the 1st electronic element of a board.